Fishing rods, as a device for casting and controlling the casting of a bait or lure attached to a retrieval line and adapted for the catching of fish, have been known since before Isaac Walton's famous first treatise on fly fishing. A fishing rod serves two major purposes:
As a spring-loaded lever having a very large speed ratio, it serves to impart a controlled tension and force to a fishing line, directing and transforming a snapping action of the hand into a whip action of the fishing line, casting a lure in a controlled manner both as to direction and, in the hands of skilled user, as to distance.
As an essentially large spring, when held substantially at right angles to the direction of tension on a fishing line while a fish is being engaged, the rod maintains, through spring-like lever action, a constant, non-jarring tension on the line and, thus, allows a substantially lightweight line to be effectively used to wear down and catch a fish which should be capable of imparting a breaking tension on the line.
Any feasible means of securing the rod would probably be suitable for the second, catching purpose. The major emphasis in rod design and in the design of handles is on providing precise, tactile feedback to aid in the very delicate process of repeatably and accurately casting a lure to a given spot using the rod. In this regard it is to be noted that the mechanical advantage of a standard six foot fishing rod, from point of pivot to outer tip is a extreme.
The average male human hand may span four inches when in a handle gripping position, from the point of pivotal rotation to the edge of the extended index finger; on a six foot fishing rod this represents an eighteen to one mechanical ratio between the motion of the tip and the motion of the hand. More importantly, the speed of manipulation of the rod, the angular momentum imparted to the handle of the rod, is a complex combination of forces. A change in angular acceleration, as by a whipping motion, is partially stored in the spring action of the rod; there is a delayed application in the motion imparted to the dynamic combination of line and lure. This spring action is a function of rod stiffness, and for the typical tapered fishing rod, is additionally a function of the varying spring rate along the length of the rod. The motion itself, that of casting, is typically of only several seconds duration; further, although human sight is the most precise of the senses, during most of the cast it is not possible for the fisherman to visually follow the motion of the entire system.
For this reason, tactile feedback becomes the principal, predominate mechanism whereby the fisherman may detect and control the speed of his cast, the energy that is held in the rod as spring-bending rather than as motion, and the movement of the rod.
However, this feedback necessarily must be extremely precise as the very same lever action which translates a relatively small wrist motion into a major increase in velocity of the lure equally reduces the feedback forces from the dynamic combination of lure, line, and rod to very small sensations of motion and pressure. Again, for a six foot rod the tactile sensations on the hand of the fisherman are reduced by the same eighteen to one ratio that the force of the user's wrist is magnified by.
For this reason, it is important in a casting rod that the fisherman be able to repeatably and accurately feel the motions and actions of the rod, the line, and the lure.
An additional factor occurs in the field of bait casting. Bait casting tends to use substantially thicker and, therefore, less flexible line than fly casting or spin casting and tends to use shorter, stiffer rods with heavier lures. The most important hand manipulation difference, results from the fact that in bait casting, the typical bait casting reel has a significant angular moment of inertia on the line and spool. The dynamics of spool operation, therefore, differ considerably from fly casting; spin casting reels were initially invented to overcome the spool inertia effect typical in bait casting. It is this spool inertia that creates overrunning and backlash should, at any time during the casting process, the rod be manipulated so that the speed with which the line feeds out ever decrease. Such a decrease results in the reel overrunning the line and jamming with a backlash.
In order to prevent this effect typical bait casters hold a fishing rod so that their thumb remains adjacent to the reel, so that thumb contact can be applied for reel control or as form of drag during casting.
Removing the thumb from an enclosing position around the rod handle changes the feel of the rod within the hand, and makes the relative tactile feedback through the fingers more important to successful casting.